This invention relates to a connecting mechanism for two members at a bicycle derailleur, and more particularly to a connecting mechanism for connecting a first member having a supporting tubular member and a second member having a shaft.
Generally, a bicycle derailleur has a base member, two linkage members and a movable member. The base member is mounted on a fork end of a bicycle frame with or without a bracket member and the movable member carries a chain change-over cage having pulleys.
When a bracket member is used, the derailleur is provided with shafts fixed to the bracket member and change-over cage and with supporting tubular members provided at the base member and movable member respectively, the shafts being inserted into the supporting tubular members so that the base member and change-over cage are swingably supported to the bracket member and movable member through respective bearings.
A coiled spring is housed within each supporting tubular member to respectively bias the base member and change-over cage unidirectionally with respect to the bracket member and movable member. During operation a control wire is manipulated so that a driving chain carried by the pulleys is switched to a selected one of the multistage sprockets provided at a hub at the bicycle.
A derailleur having the just described construction also conventionally includes a rotary connection between the supporting tubular member at the first member, such as the base member or movable member, and the shaft at the second member, such as the bracket member or change-over cage. The rotary connection contains bearings formed mainly of synthetic resin. Unfortunately,, the rotary connection is poorly sealed creating a problem in that dust or rain water can enter the supporting tubular member interfering with the lubricating oil contained therein or rusting the coiled spring, thus impeding smooth rotation of the rotary connection.
One solution to this problem would be to interpose a sealing member in the rotary connection. However, the supporting tubular members and shafts of the derailleur have rough dimensions and errors of about .+-.1 mm are common in the completed assembly. This makes it difficult to ensure a tight seal even when a sealing member of fixed size is used, because the component tolerances form gaps. Even if a tight sealing is attained, a greater resistance is then applied against rotation of the rotary connection which hinders its proper rotation. Thus, when dimensional errors exist in the component members, it is difficult to reliably seal the rotary connection while keeping the rotational resistance from increasing.
This invention has been designed to overcome the above problems. An object of the invention is to provide a connecting mechanism for two members at a bicycle derailleur which is capable of compensating for dimensional errors existing in the rotary connection at the derailleur, thereby always ensuring that the rotary connection is completely sealed while the rotational resistance is maintained under a prescribed value.
The invention is characterized by a pair of first and second bearings which are interposed between a supporting tubular member provided at a first member, such as a base member or movable member, and a shaft provided at a second member, such as a bracket member or change-over cage, at the derailleur. The first and second bearings each have a tubular portion inserted between the inner periphery of the tubular member and the outer periphery of the shaft and a flange disposed opposite to an axial end face of the supporting tubular member. At least one of the first and second bearings defines at its flange an annular groove opening at one axial side of the flange, into which groove an annular sealing member comprising elastic material is loosely fit being freely elastically deformed to compensate for errors in axial dimension in the supporting tubular member, shaft or bearings, thus eliminating the usual minimum gaps produced between the bearings and the surfaces of members slidably contacting with them.
The annular groove at the flange of the respective bearings is formed large enough to allow the sealing member to be elastically deformable within the groove. The sealing member is made larger in height than the groove and projects beyond the groove opening thereby contacting at the projecting end face with either the end face of the supporting tubular member or the second member.
With this arrangement, if a minor error exists in the axial dimension of the supporting tubular member or shaft creating a narrow gap between the end face of the supporting tubular member and the bearing or between the bearing and the second member, the sealing member is deformed in height sinking at a part of its projecting end into the groove, to compensate for the axial dimension error. On the other hand, when the gap is larger, the sealing member expands towards its full projecting height to compensate for the axial dimension error. In both the cases, the projecting end face of the sealing member contacts elastically with either the end face of the supporting tubular member or the second member to close the gap. As a result, the connecting mechanism of the invention always ensures closure of the gap without an increase in the rotational resistance applied to the connecting mechanism thereby obtaining an improved sealing effect.
These and other objects and novel features of the invention will be more apparent from the following description of an embodiment thereof described in connection with the accompanying drawings.